Discussion on mechanized construction technology o

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Discussion on mechanized construction technology of black pavement based on prevention of segregation

many asphalt pavements of expressways in China have suffered various damages in the early stage, which are closely related to the segregation of paving materials in the process of asphalt pavement construction. The causes of asphalt mixture segregation are complex, which involves all links in the construction of asphalt pavement. Therefore, reasonable control of the construction process of asphalt pavement can effectively prevent the occurrence of asphalt mixture segregation, improve the paving quality of asphalt pavement, and obtain good economic and social benefits

from a macro perspective, there are roughly three types of segregation of hot mix asphalt mixture:

(1) aggregate segregation. The improper operation of hot mixed asphalt mixture in the process of production, transportation, paving and compaction causes the coarse and fine aggregates of asphalt mixture to gather separately, resulting in obvious uneven state. The void ratio of asphalt pavement with relatively concentrated coarse aggregate is large, which leads to the reduction of water damage resistance and durability of asphalt pavement, resulting in cracks, pumping, potholes, spalling and other diseases. The asphalt pavement with concentrated fine aggregate has small voids and relatively large asphalt content, which is prone to rutting, oil flooding, waves, carbuncle and other diseases

(2) temperature segregation. Can pigs really fly during the transportation and paving of hot asphalt mixture? For the internal mass email titled, the temperature drop at different positions of the truck and paver is inconsistent, resulting in the temperature difference of the asphalt mixture, resulting in temperature segregation, making the compactness of the asphalt pavement different after rolling, resulting in cracking, settlement and other diseases

(3) aggregate asphalt segregation. Asphalt and SMA mixtures with large oil content are prone to such segregation. Due to the great harm of asphalt mixture segregation, in recent years, various construction units and scientific research institutes have started to study and improve the construction technology and quality monitoring to improve the construction quality of asphalt pavement in view of the main causes of asphalt mixture segregation

investment scope can be 1 asphalt mixture production

1.1 material selection in expressway asphalt pavement materials, different specifications of crushed stones are purchased from the market. In order to ensure the supply of raw materials, there will be multiple gravel yards supplying materials at the same time. There is no unified specification and unified crushing and screening equipment for each gravel yard, so the actual size of the gravel of the same specification produced by each gravel yard is also different. Therefore, the construction unit of highway engineering should work with the contractor to determine the quarry according to the actual needs, and use the same crusher and screening equipment to reduce the heterogeneity of raw materials. Conditional construction units can re screen the crushed stones after the raw materials enter the site

1.2 stacking

(1) prepare an aggregate yard with a solid and clean surface

clean, and the aggregate site should be drained smoothly

(3) the asphalt mixture mixing station should stack aggregates of different specifications separately, and have reliable isolation facilities to avoid mixing aggregates

(4) there are several stacking methods. It is best to stack layer by layer and gradually increase it. This layered stacking can reduce the segregation caused by the gravity of the aggregate. When the aggregate is dumped by the material truck, it should be dumped next to the surface of the pile one by one. If the lifting grab is used to accumulate the aggregate, it should be placed along one surface, one bucket by one bucket, and it is not allowed to throw

1.3 shoveling

all shoveling work will cause spalling of various aggregates to a certain extent and segregation of aggregates of different sizes. Therefore, the number of shoveling should be minimized to reduce spalling and segregation

1.4 proportion

(1) the continuous density graded asphalt mixture is easier to produce segregation than the discontinuous graded asphalt mixture, so the grading uniformity of the aggregate should be strictly controlled in the proportion design and mixing production, so that the grading error is controlled within the specified range, and close to the median value of the grading curve range required by the standard

(2) control the particle size and content of the filler to ensure that the aggregate is completely covered by asphalt. Generally, the particle size of the filler should be greater than 0.075mm, and its content should be close to the lower limit of the design

(3) control the asphalt dosage to make it within the error range required by the design

(4) mineral powder can improve the stability of asphalt mixture and avoid segregation, but the mixing amount should not be too large, and the ratio of mineral powder to asphalt should be (1:1) ~ (1:2)

(5) change the previous practice that the production proportion will not be changed once, but readjust the aggregate proportion every once in a while according to the screening results in the hot mix bin and control room, which can greatly reduce the variability of particle composition of asphalt mixture

1.5 mixing production

(1) the upper mouth of the cold hopper should be separated to avoid entering other silos when loading into a cold hopper

(2) adopt automatic discharge hopper to feed the cold aggregate evenly along the opening of the cold hopper, which can communicate with the company, so as to eliminate the bridge phenomenon leading to segregation

(3) the hot aggregate lifting device should be reasonable to prevent large aggregate from sliding from the top

(4) if the vibrating screen in the asphalt mixer is partially broken, there will be some oversized large-size aggregate in the asphalt mixture, so it should be checked frequently and replaced if necessary

(5) add a baffle on the upper part of the hot bin to make the dust slide to the middle of the bin along the baffle and mix evenly with the coarse aggregate

(6) short mixing time may lead to uneven mixing of asphalt mixture or uneven temperature, so strictly control the mixing time, pay attention to observe whether there is obvious aggregation of large aggregate and small aggregate in the asphalt mixture, and if so, find out the cause and deal with it in time; (7) Anti segregation hopper is adopted. Each finished product silo has realized the integration of informatization and industrialization earlier. There is a receiving hopper at the top, which concentrates the asphalt mixture and flows into the finished product silo, so that the asphalt mixture in the finished product silo remains at the same height without forming a cone surface, so as to avoid the segregation of the finished product

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